The present invention relates to a casing joint, particularly between a box member and a pin member with complementary threads. More particularly, the invention relates to a joint construction wherein the threaded portion of each member is divided in two axially spaced portions or thread sections with a transition zone in between. Since the two thread sections are of different diameters, a radial step is provided in that transition zone.
Casing joints for oil field equipment are known in great abundance and variety. The principal problem here is to provide a tight seal between the casing members combined with definite stops for limiting threading as the joint is made up. U.S. Pat. Nos. 2,211,179, 2,992,019, 3,100,650 and 3,359,013 are but examples for this state of the art.
Problems still exist in that the known joints do not provide for a satisfactory combination of sealing and stop functions particularly in those instances, in which multiple seals are needed. This is particularly so if one wants to avoid extremely accurate manufacturing tolerances with regard to the spacings between different sets of engaging surface portions, shoulders, end faces, etc. Also, individual matching of box and pin members which will make up the joint is not only very cumbersome, but impractical. The casing members should be used interchangeably and, possibly, repeatedly and in different combinations.